**Core Concept**
A pit latrine is a type of sanitary toilet that uses a hole in the ground to collect human waste. The depth of the pit is crucial in preventing the contamination of groundwater and maintaining a safe environment. The recommended depth of a pit latrine is based on various factors, including the population served, the type of soil, and the local regulations.

**Why the Correct Answer is Right**
The correct depth of a pit latrine depends on the population served and the type of soil. In general, a pit latrine should be at least 2.5 to 3 meters deep to prevent the contamination of groundwater. This depth allows for a sufficient separation between the pit and the water table, reducing the risk of waterborne diseases. The pit should also be constructed with a concrete slab and a cover to prevent odors and pests from escaping.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a depth of 1 meter is too shallow to prevent the contamination of groundwater.
**Option B:** This option is incorrect because a depth of 4 meters is excessive and not recommended for most pit latrines.
**Option C:** This option is incorrect because a depth of 1.5 meters is still too shallow to ensure safe and effective waste disposal.

**Clinical Pearl / High-Yield Fact**
A well-constructed and properly sized pit latrine can reduce the risk of waterborne diseases by 90%. This is because the pit provides a safe and sanitary means of waste disposal, reducing the likelihood of contamination of surface water and groundwater.

**Correct Answer: C. 2.5 - 3 meters**